1. Field
The present disclosure generally relates to metal forming, and deals more particularly with a method and apparatus for hot forming metal parts such as leading edges of airfoils.
2. Background
A process referred to as hot forming is sometimes used to form part blanks, such as metal sheets, into precise part geometries with smooth surface finishes. For example, in the aircraft industry, leading edges of airfoils such as wings and stabilizers are required to have exceptionally smooth surfaces, free of scratches, roughness and waviness in order to reduce boundary layer turbulence that causes undesirable drag. In some cases, turbulence may be further reduced by providing the airfoil with perforations in the leading edges which allow the air layer near the surface of the airfoil to be drawn in through the airfoil surface and subsequently vented to the atmosphere. The hot forming process is desirable because it does not adversely affect surface smoothness or distort airfoil perforations.
In the past, the leading edges of airfoils were hot formed using vacuum pressure and bagging film. A preformed part blank was placed on a heated, mandrel-like tool having an internal vacuum cavity. An insulation blanket was draped over the part blank, following which bagging film was installed over the insulation blanket and sealed around the tool, forming an internal vacuum chamber over the part blank. The tool was heated to a temperature sufficient to relax the part blank and allow it to be formed. A vacuum was then drawn beneath the bagging film, causing pressure to be applied to the part blank which formed the blank down over the tool. The insulation blanket insulated the hot part blank from the bagging film to prevent the bagging film from melting. This technique had a number of disadvantages. The installation and sealing the bagging film is time-consuming and labor-intensive. Additionally, the high forming temperature and applied vacuum pressure caused the insulation blanket to break down into dust-like particles which spread and settled over equipment, requiring labor-intensive cleanup. In addition, both the bagging film and the blankets are consumables which add to recurring expenses.
Accordingly, there is a need for a method and apparatus for hot forming metal parts such as leading edge airfoil skins which reduce recurring consumable costs and labor, while increasing production rates.